Can formaldehyde offgassing from OSB boards be deterred with Sheetrock and sealant?

I am planning to convert our newly built garage into a Tiny House. But, I have come to find that I have a real problem with the off gassing of formaldehyde from the OSB boards. I installed an ERV, the air exchange has been happening for several weeks now, but the fumes are just as troublesome. My next plan is to paint the boards with SafeCoat Safe Seal.

My question is can airtight sheet rocked walls and ceilings, prevent the formaldehyde from passing through, if the SafeCoat doesn't hold it all in? And, should I put a plastic or some other material layer just under the sheetrock to help seal it?

Also, I had the garage tested for formaldehyde, the level is 0.011, which I'm told is high enough to attempt to mitigate.

1 Answer

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Diane,
I'm not an expert on formaldehyde, but your reference to 0.011 confuses me. You don't give the units. Most results are reported as either parts per million (ppm) or parts per billion (ppb).

One source reports that older homes have average formadehyde concentrations that are generally well below 0.1 (ppm). In homes with significant amounts of new pressed wood products, formaldehyde levels can be greater than 0.3 ppm.

Another source reports that California homes have an average indoor formaldehyde level of 200 parts per billion (0.2 ppm).

There are several issues that need to be determined in your case:

1. What is the measured level of formaldehyde in the air in your garage?

2. Are you sure that you know where the formaldehyde is coming from?

If you are sure that the source of the formaldehyde is the OSB, then I would advise (1) installing an interior air barrier (for example, by following the Airtight Drywall Approach, a method that requires the use of airtight electrical boxes), and (2) installing an exhaust ventilation system that continually exhausts the space at the rate recommended by ASHRAE 62.2 (7.5 cfm per occupant plus 1 cfm for every 100 square feet of occupiable floor area).